Reaction of Propylene with Formaldehyde*

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1 Reaction of Propylene with Formaldehyde* Kenichi Fukui,** Toshio Takino** and Hisao Kitano** Summary: The reaction of propylene with formaldehyde in acetic acid solution catalyzed by sulfuric acid is studied. The optimum mole ratio of sulfuric acid to formaldehyde is found to be about 0.2 and the favorable acid containing 30 vol % of acetic anhydride serves as a suitable solvent. The products are 4-methyl-1, 3-dioxane, 1, 3-butanediol diacetate and 4-acetoxytetrahydropyran, and the former two of these compounds can be converted to pyran derivatives via allylcarbinol acetate. However, the formation of 4-acetoxytetrahydropyran from propylene and formaldehyde by the Prins reaction may be explained by the Baker's mechanism of hyperconjugation of the propylene methyl radical without considering the formation of allylcarbinol acetate. Various reactions of 4-hydroxytetrahydropyran are carried out and its derivatives are prepared, including several new compounds. For the sake of comparison with the reactivity of propylene, some reactions of allyl halides with formaldehyde are also studied and the main products are found to be 4-halomethyl-1, 3-dioxanes. Introduction What is called the Prins reaction, the condensation of olefins and aldehydes, is generally accelerated by catalysts, heat and light. The reaction of propylene with formaldehyde was investigated by some workers, i. e. by Fitzky,1) Baker,2) Hamblet3) and Arundale,4) since Our previous paper5) has shown that propylene reacted with formaldehyde in acetic acid in the presence of various catalysts, e. g. sulfuric acid, perchloric acid and boron trifluoride, to yield 4-methyl-1, 3-dioxane, 1, 3-butanediol diacetate and 4-acetoxy-tetrahydropyran. In the case of perchloric acid catalyst, 4-methyl- 1, 3-dioxane was obtained in good yields, whereas boron trifluoride and sulfuric acid catalysts favored the formation of 1, 3-butanediol diacetate. Recently, the Prins reactions of this type have attracted attention from the point of the utilization of lower olefins and aldehydes from petrochemical industry.6) In the present work, the reaction of propylene with formaldehyde * Received November 14, This work is supported financially in part by a grant-in-aid from the Ministry of Education. Japanese Government. ** Department of Fuel Chemistry, Faculty of Engineering, Kyoto University, Sakyo-ku, Kyoto. catalyzed by sulfuric acid is systematically studied to elucidate the reaction conditions to obtain good yields of desired products. Additional experiments are made with regard to the reactions of pyran derivatives. The reactions of some allyl halides with formaldehyde are also studied. Propylene under atmospheric pressure is bubbled into a suspension of paraformaldehyde in the mixture of sulfuric and acetic acids Volume 3-March 1961.

Fukui, Takino and Kitano: Reaction of propylene absorbed is but little changed with the mole ratio of sulfuric acid to formaldehyde in the range from 0.16 to 0.48. Practically, the mole ratio of ca.

2 Fukui, Takino and Kitano: Reaction of propylene absorbed is but little changed with the mole ratio of sulfuric acid to formaldehyde in the range from 0.16 to Practically, the mole ratio of ca. 0.2 is recommended. Although the maximum absorption of propylene higher temperature. The propylene absorption can be accomplished more efficiently in a mixture of acetic acid and acetic anhydride than in acetic acid only. The highest yield of the products is obtained in the mixture of acetic acid containing 30 vol. % anhydride. In this optimum condition, 4-methyl- 1, 3-dioxane, 4-acetoxytetrahydropyran and 1, 3-butanediol diacetate are formed in the ratio of about 2:5:10. In the case of more than 50% of the acetic anhydride content in the solvent, the product is mainly methylene diacetate, which is also found to be prepared in good yields from acetic anhydride and paraformaldehyde in the presence of boron trifluoride complexes. Methylene diacetate will not react with propylene under atmospheric pressure, but when utilized as a solvent for the reaction of propylene with formaldehyde, a similar result to the case of acetic acid, was obtained. 4-Acetoxytetrahydropyran is readily hydrolyzed to lead 4-hydroxytetrahydropyran.2) Preparation of 4-hydroxytetrahydropyran without the use of propylene was carried out by the condensation of allylcarbinol with formaldehyde7)8) or by the reduction of nyrone-4.9) 4-Acetoxytetrahydropyran formed by the above-mentioned Prins reaction can be derived from 1, 3-butanediol diacetate through allylcarbinol acetate, since allylcarbinol or its acetate was synthesized by the elimination of 1, 3- butanediol or its diacetate7)8). However, the formation of allylcarbinol acetate from 1, 3-butanediol diacetate and the condensation of allyecarbinol acetate with formaldehyde require a high temperature and is not usable in the reaction of propylene with formaldehyde. For instance, the elimination of 1, 3-butanediol diacetate (prepared by boiling 4- methyl-1, 3-dioxane with acetic acid-acetic anhydride mixture in the presence of sulfuric acid) can be barely made by distillation in the presence of p-toluenesulfonic acid. 4-Acetoxytetrahydropyran is prepared by refluxing the mixture of allylcarbinol acetate and paraformaldehyde in acetic acid in the presence of sulfuric acid. The experimental facts mentioned above indicate that the formation of pyran derivatives from propylene and formaldehyde may be explained by Baker's mechanism2) involving the hyperconjugation of methyl radical of propylene. Products, other than pyran derivatives, from Prins reaction of propylene and formaldehyde can also be converted to pyran derivatives through a few steps. Hence, the Prins reaction of this kind is considered as an interesting means to prepare pyran derivatives. Some new urethans, tetrahydropyrone-4, and its derivatives are also prepared from 4-hydroxytetrahydropyran. Allyl fluoride, allyl chloride, allyl bromide, and methallyl chloride instead of propylene were brought into reaction with formaldehyde to obtain 4-halomethyl-1, 3-dioxanes (4-methylchloromethyl-1, 3-dioxane in the case of methallyl chloride) as the main products and some high-boiling substances as by-products. Bulletin of The Japan Petroleum Institute

3 Propylene with Formaldehyde Experimental 1. Relation between the amount of propylene absorbed and the concentration of sulfuric acid: In a flask fitted with a mercury-sealed mechanical stirrer, thermometer, reflux condenser and gas inlet, were placed 19g (0.63 mol.) of 60 mesh powdery paraformaldehyde, 100cc of glacial acetic acid and 98% sulfuric acid whose amount was indicated in Table 1. Twenty six grams (0.62mol.) of purified propylene in 4hrs was introduced into the mixture while stirring and the reaction temperature propylene absorbed was measured by the increased weight of the mixture. The results obtained are shown in Table Separation of the products: The reaction mixture containing propylene absorbed was cooled, neutralized with aqueous sodium carbonate solution, and extracted with ether. The ethereal solution was washed with aqueous sodium chloride, dried with anhydrous sodium sulfate and fractionally distilled. Redistillations of each fractions gave the results shown in Table Reaction solvents: The reactions were carried out in the same manner as described in 1. utilizing the solvents shown in Table 4. One hundred cc of each solvent and 20g. (0.2mol.) of 98% sulfuric acid were employed. The reaction mixture was separated and purified by the same treatment as described in 3. The results obtained are shown in Table 4. Table 1. Relation between the Amount of Propylene Absorbed and the Mole Ratio of Sulfuric Acid to Formaldehyde 2. Relation between the amount of propylene absorbed and the reaction temperature: The reactions were carried out in the same manner as described in 1. In this experiment 20g of 98% sulfuric acid was employed as a catalyst and 26g of purified propylene was introduced in 2hrs. The amount of propylene absorbed in the experiments at various temperatures are shown in Table 2. Table 2. Relation between the Amount of Propylene Absorbed and the Reaction Temperature. 5. Methylene diacetate: Although methylene diacetate was prepared from the reaction of acetic anhydride with formaldehyde in the presence of zinc chloride,10) sulfuric acid11) and cation-exchange resin,12) the yields were not so high. In the present work, boron trifluoride complex was used as a catalyst by the following procedure to obtain the product in good yields. In a three-necked flask fitted with a stirrer, reflux condenser and thermometer, 140g (4.67mol.) of paraformaldehyde, 840cc of acetic anhydride and 3.5cc of boron trifluoride etherate were placed and gently heated while stirring, until the was kept at this temperature for 30 minutes for reaction. After the reaction mixture was cooled, the mixture was poured into water and extracted with ether. The ethereal solution was dried over anhydrous sodium sulfate and distilled to give 435g (71% yield) of Hg, n20d ). Although methylene diacetate hardly reacts with propylene in the presence of sulfuric acid catalyst at ordinary pressure, it was used as one of the solvents, in place of acetic acid, in the reaction of propylene with formaldehyde to afford a result similar to run No. 1 in Table , 3-Butanediol diacetate: The fraction III described in 3. consisted of 1, 3-butanediol diacetate. This compound can also be prepared from 4-methyl-1, 3-dioxane of the fraction I of 3. In a flask equipped with a reflux condenser Volume 3-March 1961.

4 Fukui, Takino and Kitano: Reaction of Table 3. Separation of the Reaction Products. Table 4. Reaction Solvents. were placed 136g (1.33mol.) of 4-methyl-1, 3-dioxane, 150g of acetic acid, 150g (1.47 mol.) of acetic anhydride and 6g of 98% sulfuric acid. After refluxed for 7hrs. the mixture was cooled, poured into cold water and extracted with benzene. The benzene extract was dried over anhydrous sodium sulfate and distilled to yield 161g 7. Allylcarbinol acetate: A flask fitted with the Widmer column containing 50g of 1, 3-butanediol diacetate and 2.5g of p-toluenesulfonic acid was heated to maintain the distillation temperature in the 9. 4-Hydroxytetrahydropyran: 49g, was washed with aqueous sodium carbonate solution and extracted with ether. The ethereal solution was washed with saturated aqueous sodium chloride solution and distilled. Allylcarbinol acetate 17g (52% yield) was 8. 4-Acetoxytetrahydropyran: In a flask fitted with a mercury-sealed stirrer, reflux condenser, thermometer and dropping funnel, 31.6g (1.05mol.) of paraformaldehyde, 250cc of glacial acetic acid and 2g of 98% sulfuric acid were placed. The mixture was strirred and gently warmed. Through the dropping funnel 120g (1.05mol.) of allylcarbinol acetate was added into the mixture, and the ditional 5hrs. After cooled, the resultant mixture was washed with water and extracted with benzene. The extract was dried with anhydrous sodium sulfate and distilled to give 58g (38%) of crude 4-acetoxytetrahydropyran were also obtained. These fractions were redistilled and their physical constants were compared with those obtained by other workers. These results are shown in Table 5. After the mixture of 100g (0.69mol.) of 4-acetoxytetrahydropyran, 250cc of methanol and 50cc of 12N hydrochloric acid was refluxed in a water bath for 5hrs., the formed methyl acetate was distilled off and the residue was neutralized and dried with sodium carbonate. The distillation gave 46g (65%) of 4-hydroxy Tetrahydropyranol chloroformate: Into a Claisen flask equipped with a gas inlet containing 50cc (0.5mol.) of 4-hydroxytetra- Bulletin of The Japan Petroleum Institute

5 Propylene with Formaldehyde hydropyran, purified phosgene war gently introduced at room temperature. After the increased weight of the mixture reached about 35g, the unreacted phosgene and hydrogen chloride were removed on a water bath, and the remaining liquid was distilled under atmospheric, to give 61g of 4-tetrahydropyranol potassium bichromate dissolved in 50cc of water Anal. Calcd. for C6H9O3Cl: Cl, After the addition was completed, the reaction Found: Cl, Urethans of 4-hydroxytetrahydropyran: 4-Tetrahydropyranol chlorofomate 1.6g (0.01 mol.) obtained in 10. was allowed to react with 0.02 mole of several amines shown in mixture was poured into diluted hydrochloric acid, and the resultant precipitate was collected. Recrystallization from ligroin or ethanol yielded crystalline urethans. These new compounds were shown in Table 6. They are useful for the identification of 4-hydroxytetrahydropyran. 12. Tetrahydropyrone-4: To the solution of 10g (0.1mol.) of 4-hydroxytetrahydropyran dissolved in 500cc of 30% sulfuric acid, was added slowly 15g of temperature for 1hr. The green solution was cooled and extracted with ether. The ether layer was dried with sodium carbonate and was redistilled and yielded 2g (20%) of tetrahydropyrone-4 with a pleasant odor, which the following compounds shown in Table 7 in the usual manner. Table 5. Products from the Reaction of Allylcarbinol Acetate with Formaldehyde. Table 6. Urethans of 4-Hydroxytetrahydropyran. Table 7. Derivatives of Tetrahydropyrone-4. Volume 3-March 1961.

6 Fukui, Takino and Kitano: Reaction of Propylene with Formaldehyde Table 8. Reaction of Allyl Halides with Formaldehyde. 13. Reactions of allyl halides with formaldehyde: The reaction was carried out with 0.62 mole of allyl fluoride, allyl chloride, allyl bromide and methallyl chloride, respectively, in the similar manner, instead of using propylene. The compounds shown in Table 8 were obtained as the main products. For comparison's sake, ethylene was also used as the starting olefin instead of allyl halide. In this case trimethyleneglycol diacetate (b. p. 1, 3-Butanediol diacetate and its formal are useful as solvents or intermediates for the synthesis of organic chemicals. But with regard to the use of pyran derivatives, we should expect the future development to afford some interesting problems. References 1) W. Fitzky, U. S. P. 2,124,851 (1938); 2,143,370 (1939); 2,325,760 (1943). 2) J. W. Baker, J. Chem. Soc., 1944, 296. the reaction of vinyl bromide with formaldehyde in an autoclave resulted in the formation 3) C. H. Hamblet, A. McAlevy, U. S. P. 2,426,017 (1947). 4) L. A. Mikeska, U. S. P. 2,307,894 (1943); E. Arundale, L. A. Mikeska, U. S. P. 2,350,485 (1944); R. naldehyde (2, 4-dinitrophenylhydrazone m. p. Rosen, E. Arundale, U. S. P. 2,368,494. (1945); 2,504,732 (1950). mmhg), but 1, 3-dioxane derivative was not 5) K. Fukui, Y. Ooe, H. Kitano, J. Chem. Soc. Japan isolated. Ind. Chem. Section, 62, 1667 (1959). 6) A. T. Blomquist, J. A. Verdol, J. Am. Chem. Soc., 77, 78 (1955); N. C. Yang, D. D. H. Yang, C. B. Conclusion Ross, ibid., 81, 133 (1959). In the condensation reaction of lower olefins 7) E. Hanschke, Chem. Ber., 88, 1053 (1955). with formaldehyde, diol (or its ester) and its 8) M. I. Farverov, E. P. Tepenitsyna, N. K. Shemyakina, Doklady Akad. Nauk. S. S. S. R., 99, 793 (1954); cyclic formal or their mixture are generally formed, while in the case of propylene, a pyran Zhur. Obschchei Khim., 25, 133 (1955); Chem. Abst., 49, 8315 (1955). derivative is additionally obtained as one of 9) O. Heuberger, L. N. Owen, J. Chem. Soc., 1952, the main products. In our previous paper5) 910. it was reported that the formation of pyran 10) M. Descude, Ann. chim. phys., (7), 29, 502 (1903). derivatives should be noted in respect to the 11) R. Wegscheider, E. Spath, Monat. Chem., 30, 841 application of the Prins reaction to the synthetic (1909). chemical industry employing propylene. 12) S. Yamada, I. Chibata, R. Tsurui, Pharm. Bull., In the present work, a further study was 2, 62, (1954). made in some details with respect to this observation to point out that the formation of pyran 13) H. Staudinger, R. Signer, D. Russidis, Ann. 474, 145 (1927). 14) J. D. Roberts, V. C. Chambers, J derivatives is characteristic of the reaction of. Am. Chem. Soc., 73, 5039 (1957). propylene with formaldehyde, and that 1, 3-15) S. Olsen, Acta. Chem. Scand., 4, 901 (1950). butanediol diacetate can be converted to 4-16) S. Olsen, G. Aksnes, ibid., 4, 993 (1950). acetoxytetrahydropyran through a few steps. 17) R. H. Hall, S. Stern, J. Chem. Soc., 1950, 494. Bulletin of The Japan Petroleum Institute

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